The increased use of fireplaces and stoves for home heating in recent years has greatly increased the risk of fire because of the creosote deposited in the flue as the gases cool on their way up the chimney. It is not unusual for the hard tenacious deposit to reach a thickness of several inches in one heating season so as to reduce the cross-sectional area of an eight-inch flue to a few square inches. The variation in thickness of the deposit depends on a number of factors, but the thickest portion is usually several feet above the damper of a fireplace or the point where the pipe from a stove enters the chimney. Once the deposit is ignited, it becomes so hot that it can cause the building to catch fire. For these reasons, it is recommended that the creosote deposit be removed at least once a year, and preferably more often. However, because of the difficulty of using presently available flue-cleaning equipment, this is not generally done.
Three different types of apparatus have been suggested for cleaning flues. In a first type that is the one generally available, a scraper is moved up and down the flue. Examples of such apparatus are described in U.S. Pat. Nos. 1,256,402; 2,058,112; 4,353,143 and 4,128,758. In the first three patents, the scraper is mounted on the end of a shaft which is inserted in the chimney and pushed and pulled by the operator; and in the last patent, a permanent pulley system is installed at the top of the chimney whereby the scraper can be raised and lowered. With the scraper mounted on a shaft, the shaft must be so stiff in order to exert the required force on the scraper that it cannot easily bend around corners such as would be necessary if it were inserted into the flue through the damper of a fireplace or through a clean-out door at the bottom of the chimney. In most cases, this makes it necessary to insert the scraper through the top of the chimney so as to require the operator to climb on the roof. For many people this is practicably impossible and for all except those with considerable experience it presents a great risk of serious injury. Even a skilled person can inadvertently damage the roof. Furthermore, if the chimney has a cap, it must be removed before this procedure can be used.
Whereas these scraping devices may be of some use when the deposit in the flue is relatively thin, they are practically useless when the deposit is thick because if the scraper itself is stiff enough to remove a thin hard deposit from the flue, it is extremely difficult to move it along the flue where the deposit is thick. In fact, if there is a sudden restriction due to the creosote deposit, it may not be possible to move the scraper past it. Therefore, it will generally be necessary to climb on the roof and chip off the deposit with a stiff rod until the scraper can be made to pass through the flue. Scrapers are therefore capable of making the finishing touches but are not very helpful in doing the basic job.
Some scraping devices presently on the market have outwardly extending stiff prongs and are designed to have a rope attached to each end. In use, an operator on the roof pulls on one rope so as to move the device upward through the flue and another operator at the bottom of the chimney pulls on the other rope so as to move the device downward. Quite often, the device becomes stuck so that it is difficult to move it either way.
An additional disadvantage of this first type of device is that the cross-section of the scraper must fit the cross-section of the flue, thus requiring different expensive devices for flues of different sizes and shapes.
In a second type of device, the center of a circular brush is mounted coaxially on a shaft that is rotated, e.g., U.S. Pat. Nos. 589,012; 2,430,512; and 2,469,821. As with the first type of device, it is difficult or impossible to remove thick deposits. This is especially true when the thickness of the deposit suddenly increases because only the ends of the bristles of the brush can remove the deposit and they cannot be brought into contact with it. In such cases, the deposit must be dislodged by chipping it with a stiff rod from the top of the chimney. In addition to requiring brushes of different diameters for different sizes of flue, this type of device does not remove creosote from the corners so that the interior of a heavily encrusted flue has a circular cross-section when the operation is finished. The creosote left on the corners still presents a fire hazard. Even with stiff brushes, the deposit is so hard that a long time is required to wear it down.
In a third type of device, chains are attached to a shaft that is rotated so as to throw the end portions of the chains against the interior of the flue by centrifugal force, e.g., U.S. Pat. Nos. 1,917,383 and 3,120,020. Even though a flexible shaft is used so as to permit insertion of the chains beyond a point of curvature, e.g., the right angle bend that must be negotiated when the end of the shaft is inserted in the vertical clean-out door usually found at the bottom of a chimney, no centering of the end of the shaft occurs because the interior of the chimney cannot exert an inward force on a chain that will be transmitted to the shaft so as to center it. Furthermore, experiments have shown that there is a strong tendency for the chains to become wrapped around the shaft, thus forming a mass that bounces from one point to another on the flue in random fashion.